Smart and autonomous growing rod for treating spinal deformities

ABSTRACT

An implantable growing rod assembly adapted to be secured along a length of a spine for treating deformities of the spine. The assembly includes a housing, a fixed rod extending along a longitudinal axis away from the housing, and an expansion rod extendible from the housing along the longitudinal axis. A driver assembly is fixed to the housing and adapted to translate the expansion rod along the longitudinal axis. Examples of the implantable growing rod assembly include a smart growing system, and an autonomous growing rod system.

FIELD OF THE INVENTION

The present invention generally relates to a growing rod for treatingspinal deformities, and more particularly to a growing rod that can besecured to a spine of a patient and manually or automatically extendedto grow with the patient's spine.

BACKGROUND OF THE INVENTION

Scoliosis is a term used to describe any abnormal, sideways curvature ofthe spine. The most common form of scoliosis for patients between theage of 10 and 18 years is termed adolescent idiopathic scoliosis (AIS).Although the particular cause of this type of scoliosis is stillunknown, advancements in the medical field have enabled doctors toincrease the likelihood of successfully treating scoliosis in childrenand adolescents.

Studies have shown that curvatures in the spine progress during therapid growth period of children. Because of this, children sufferingfrom scoliosis are generally recommended by their doctor to undergosurgical treatment to prevent curve progression and to obtain some curvecorrection.

One type of spinal surgery for treating scoliosis in children is the useof implantable rods that allow for the continued growth of the spine.One or two rods are implanted into the child through the back of thespine. The rods are then secured to the spine above and below the curveusing hooks or screws. Because the child will continue to grow after thespinal surgery, the child will be required to return every few months tohave the rods lengthened to keep up with his/her growth.

There thus exists a need to provide improved growing rods.

SUMMARY OF THE INVENTION

This Summary is provided to introduce a selection of concepts in asimplified form that are further described below in the DetailedDescription. This Summary is not intended to identify key features oressential features of the claimed subject matter, nor is it intended tobe used to limit the scope of the claimed subject matter.

The present invention cures some of the deficiencies in the prior art byproviding a growing rod that is less complex and that can be manuallyextended by a user.

The present invention provides for a minimally invasive growing rodsystem to reduce complications associated with repeated open surgeriesfor populations that are not served by current growing rods, such asMAGEC rods, because of lack of tactile feedback, stiff or hyperkyphoticdeformities, or need for frequent medical imaging such as Mills.

The growing rod of the illustrative embodiment of the present inventionis adapted to be subcutaneously implanted and secured along a length ofa spine of a patient. The growing rod comprises a fixed rod, anextendible rod having a distal portion that is slidably coupled to thefixed rod and arranged with a drive gear mechanism, and a distractionunit.

The distraction unit provides one or more mechanical elements tofacilitate linear movement of the extendible rod relative to the fixedrod. In general, the distraction unit comprises: (i) a housing attachedto the fixed rod, (ii) a rotatable drive interface accessible by anexternal driver from outside of the housing or an internal driver frominside the housing, and (iii) a drive gear mechanism housed within thehousing and coupled to the rotatable drive interface and the drive gearmechanism such that rotation of the rotatable drive interface causeslinear movement of the extendible rod through the drive gear mechanism.

Because the patient is likely to continue to grow after implantation ofthe growing rod, the patient will be required to return to the doctor(e.g., two months, four months, six months, etc., after each doctor'svisit) to have the growing rod extended in order to keep up with thepatient's growth. This can be accomplished by making a small incision onthe patient's back to access the rotatable drive interface with anexternal driver. The rotatable drive interface is adapted to bephysically coupled to and manually rotated by the external driveremployed by the doctor. As the doctor rotates the rotatable driveinterface in a first direction (e.g., clockwise), it causes linearmovement of the extendible rod through the drive gear mechanism. Thelinear movement is a result of a gear in the drive gear mechanismcooperating with the drive gear mechanism to linearly move theextendible rod relative to the fixed rod. A locking mechanism housedwithin the housing is configured to latch onto the drive gear mechanismto prevent the rotatable drive interface from being able to rotate in asecond direction (e.g., counter-clockwise) for retracting the extendiblerod. The locking mechanism also provides a means to prevent the drivegear mechanism from causing the extendible rod from retracting under thepressure of the spine; for example, when the patient is sitting up,standing, walking, etc.

By providing a manually operated implant that is less complex, like thegrowing rod of the illustrative embodiments, fewer elements and movingparts can be used to extend and retract the implant without the need ofa power source.

In still a further alternative embodiment, an implantable growing rodassembly is adapted to be secured along a length of a spine for treatingdeformities of the spine. The assembly includes a housing, a fixed rodextending along a longitudinal axis away from the housing, and anexpansion rod extendible from the housing along the longitudinal axis. Adriver assembly is fixed to the housing and adapted to translate theexpansion rod along the longitudinal axis.

In, yet still a further embodiment, a fully autonomous growing rodsystem is described to reduce complications associated with repeatedopen surgeries for populations that are not served by currentlyavailable growing rods because of lack of real-time feedback and/orhaving limited access to hospitals and surgical centers.

These advantages of the present invention will be apparent from thefollowing disclosure and the appended claims.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects, features, and advantages of the present device willbecome more fully apparent from the following detailed description, theappended claims, and the accompanying drawings in which like referencenumerals identify similar or identical elements.

FIG. 1 a top perspective view of dual growing rods, which areimplantable to treat spinal deformities, in accordance with anillustrative embodiment of the present invention;

FIG. 2 a side elevational view of the growing rod assembly of FIG. 1 ina contracted position, in accordance with an illustrative embodiment ofthe present invention;

FIG. 3 is a side elevational view of the growing rod assembly in anexpanded position of FIG. 2 , in accordance with an illustrativeembodiment of the present invention;

FIG. 4 is an enlarged top view of the growing rod assembly of FIGS. 2and 3 , in accordance with an illustrative embodiment of the presentinvention;

FIG. 5 is an exploded perspective view of the growing rod assembly ofFIGS. 2-4 , in accordance with an illustrative embodiment of the presentinvention;

FIG. 6 is an enlarged side elevational view of the gear assembly of thegrowing rod assembly of FIGS. 2-5 , in accordance with an illustrativeembodiment of the present invention;

FIG. 7 is an enlarged side elevational view of the gear assembly of thegrowing rod assembly of FIG. 6 with the housing omitted in an unlockedor neutral position, in accordance with an illustrative embodiment ofthe present invention;

FIG. 8 is an enlarged side elevational view of the gear assembly of thegrowing rod assembly of FIG. 6 with the housing omitted in a locked orengaged position, in accordance with an illustrative embodiment of thepresent invention;

FIG. 9 is a cross-sectional view of the implantable expansion rodassembly of FIGS. 2-5 , in accordance with an illustrative embodiment ofthe present invention;

FIG. 10 is a side cross-sectional view, in section, of the rod assemblyof FIGS. 2-5 , with the extendible rod in a contracted position, inaccordance with an illustrative embodiment of the present invention;

FIG. 11 is a side elevation view of the rod, in section, assembly ofFIGS. 2-5 , with the extendible rod in an extended position, inaccordance with an illustrative embodiment of the present invention;

FIG. 12 is an example of an implant driver torque wrench with Bluetoothcapabilities, in accordance with an illustrative embodiment of thepresent invention;

FIG. 13 is an input torque table illustrating adjustments made overtime, in accordance with an illustrative embodiment of the presentinvention;

FIG. 14 , this is similar to FIG. 8 described above with twopiezoelectric sensors and an electrical interface, in accordance with anillustrative embodiment of the present invention;

FIG. 15 is a simple circuit of a charge amplifier circuit to measureforces on piezoelectric sensors of FIG. 14 , in accordance with anillustrative embodiment of the present invention;

FIG. 16 is an input torque and expansion rod force table illustratingadjustments made over time, in accordance with an illustrativeembodiment of the present invention;

FIG. 17 is an example graph showing the values in the table of FIG. 16 ,in accordance with an illustrative embodiment of the present invention;

FIG. 18 is a block diagram of an autonomous growing rod motor-drivenimplant, in accordance with an illustrative embodiment of the presentinvention; and

FIG. 19 is a flow chart of the sensor interpretation used to control thegrowing rod motor-driven implant of FIG. 18 .

DETAILED DESCRIPTION

In the drawings, like numerals indicate like elements throughout. Forconvenience, the first digit of a reference number refers to the figurenumber in which it was first introduced. For example, callout number lxxis first introduced in FIG. 1 , whereas callout number 8 xx was firstintroduced in FIG. 8 . Certain terminology is used herein forconvenience only and is not to be taken as a limitation on the presentdevice. The terminology includes the words specifically mentioned,derivatives thereof, and words of similar import.

The embodiments illustrated below are not intended to be exhaustive orto limit the device to the precise form disclosed. These embodiments arechosen and described to best explain the principle of the device and itsapplication and practical use and to enable others skilled in the art tobest utilize the device.

Non-Limiting Definitions

Reference herein to “one embodiment” or “an embodiment” means that aparticular feature, structure, or characteristic described in connectionwith the embodiment can be included in at least one embodiment of thedevice. The appearances of the phrase “in one embodiment” in variousplaces in the specification are not necessarily all referring to thesame embodiment, nor are separate or alternative embodiments necessarilymutually exclusive of other embodiments. The same applies to the term“implementation.”

As used in this application, the word “exemplary” is used herein to meanserving as an example, instance, or illustration. Any aspect or designdescribed herein as “exemplary” is not necessarily to be construed aspreferred or advantageous over other aspects or designs. Rather, use ofthe word is intended to present concepts in a concrete fashion.

Additionally, the term “or” is intended to mean an inclusive “or” ratherthan an exclusive “or.” That is, unless specified otherwise or clearfrom context, “X employs A or B” is intended to mean any of the naturalinclusive permutations. That is, if X employs A; X employs B; or Xemploys both A and B, then “X employs A or B” is satisfied under any ofthe foregoing instances. In addition, the articles “a” and “an” as usedin this application and the appended claims should generally beconstrued to mean “one or more” unless specified otherwise or clear fromcontext to be directed to a singular form.

Unless explicitly stated otherwise, each numerical value and rangeshould be interpreted as being approximate as if the word “about” or“approximately” preceded the value of the value or range.

The use of figure numbers and/or figure reference labels in the claimsis intended to identify one or more possible embodiments of the claimedsubject matter in order to facilitate the interpretation of the claims.Such use is not to be construed as necessarily limiting the scope ofthose claims to the embodiments shown in the corresponding figures.

It should be understood that the steps of the methods set forth hereinare not necessarily required to be performed in the order described, andthe order of the steps of such methods should be understood to be merelyexemplary. Likewise, additional steps may be included in such methods,and certain steps may be omitted or combined in methods consistent withvarious embodiments of the present device.

Although the elements in the following method claims, if any, arerecited in a particular sequence with corresponding labeling unless theclaim recitations otherwise imply a particular sequence for implementingsome or all of those elements, those elements are not necessarilyintended to be limited to being implemented in that particular sequence.

Also, for purposes of this description, the terms “couple,” “coupling,”“coupled,” “connect,” “connecting,” or “connected” refer to any mannerknown in the art or later developed of joining or connecting two or moreelements directly or indirectly to one another, and the interposition ofone or more additional elements is contemplated, although not required.

Overview of Growing Rod Assembly for Treating Spinal Deformities

FIG. 1 a top perspective view of growing rod system 100 with dualgrowing rod constructs 190, 192, which are implantable to treat spinaldeformities, in accordance with an illustrative embodiment of thepresent invention. These special implantable spinal growing rods allowfor continued controlled growth of the spine 10. Rods are attached tothe spine above and below the spinal curve with pedicle screws 102, 104,106, 108, 172, 174, 176, 178, as shown. The rotatable drive interface104,142 are then turned with drive tool 150 to lengthen the expansionrods 120, 122, and surgically extend the patient's spine during aprocedure required every six months.

Each of the growing rod assemblies 190, 192 is generally comprised ofthree major sections. The first section is an extendible rod orexpansion rod 120, 122. The expansion rod is mechanically coupled to adistraction unit housing 130, 134. The distraction unit housing 130, 134is mechanically coupled to a third section, a base rod or fixed rod 132,136. The distraction unit housing 130, 134 includes rotatable driveinterface 140, 142. Also shown is a drive tool 150 for engaging with therotatable drive interface 140, 142 to lengthen or shorten each of thegrowing rod assemblies 190, 192.

In some embodiments, as shown in FIG. 1 , the growing rod assembly 190,192 can be affixed to a spine 10 via one or more pedicle screws 102,104, 106, 108, and 172, 174, 176, 178. The pedicle screws 102, 104, 106,108 and 172, 174, 176, 178 may be in the form of fasteners having atulip or coupling body such as those described in U.S. Pat. No.9,750,542, which is incorporated by reference herein. The growing rodassembly 190 can be implanted in either up or down position and can beused singularly or in pairs. The growing rod assembly 190 can be engagedin some embodiments through a small incision aligned with the rotatabledrive interface 140,142 (e.g., hexalobular drive interface).

In some embodiments, the bevel gear assembly provides a reduction ratioof 0.8:1 or more. In some embodiments, the bevel gear assembly providesa reduction ratio of 1:0.75 such that for every full revolution of thebevel pinion gear 534 (See FIG. 5 ), a drive output gear 746 (See FIG. 7) rotates 0.75 revolutions. In an embodiment, the ratio of the pinionteeth to the bevel gear teeth is 15:20. In an embodiment, the bevelpinion gear 534 is rotated about one (1) complete revolution to achievebetween about 1 mm and 1.25 mm of expansion or contraction of theexpansion rod 520 from distraction unit housing 130, 134, with theamount of growth based upon a goal measure of 1.8 cm to 2.4 cm per year.Advantageously, a surgeon can fine-tune the amount of expansion byeither increasing or decreasing the number of rotations. This allows thesurgeon to expand the expansion rod 520 against large forces caused bythe deformity. If a surgeon feels too much distraction has beenincorporated, the distraction unit housing 130 can be reduced by simplyreversing the direction the bevel pinion gear 534 is turned.

Advantageously, the growing rod assembly 190, 192 can be implanted viause of pedicle screws 102, 104, 106, 108, and 172, 174, 176, 178. Asshown in FIG. 1 , two pedicle screws 102, 104, 106, 108 are used ateither end of the growing rod assembly 190, 192 on the fixed rod 132,136 and the expansion rod 120, 122 to secure the growing rod assembly190, 192 to a patient's spine 10. After implantation, the growing rodassembly 190, 192 is engaged through a small incision aligned with therotatable drive interface 140, 142 of the bevel pinion gear assembly144, 146 with the specified distraction tool or drive tool 150.

The growing rod assembly 190, 192 can be implanted at any position alongthe spine 10 with the expansion rod 120, 122 either caudal or cephaladand can be used singularly or in pairs (as shown in FIG. 1 ) dependingon surgeon discretion. The length of the expansion rods 120, 122 areoversized to allow the surgeon to cut, bend and customize the expansionrod 120, 122 depending on patient anatomy. The growing rod assembly 190,192 is designed to allow for an estimated minimum of three and a halfyears of growth before replacement or removal is required. As shown inFIG. 2 , in an embodiment, the growing rod assembly 190, 192 is 600 mmlong with the expansion rod 120, 122 in a fully retracted position, andas shown in FIG. 3 , in an embodiment, the growing rod assembly 190, 192is 660 mm long with the expansion rod 520 in a fully extended position,allowing for up to 60 mm of growth of the patient.

In some embodiments, the growing rod assembly 190, 192 will have thestrength of a conventional rod and can be adjusted via a minimalincision. By using the pinion gear assembly 144, 146, a controlledadjustment can be accomplished, and distraction forces can be easilymet. In some embodiments, the growing rod assembly 190, 192 can bemanufactured using a metal, such as steel, cobalt chrome, or titanium orother suitable biocompatible materials.

High-Level View of Growing Rod Assembly

FIG. 2 is a first perspective view of a growing rod assembly 200 of FIG.1 in a contracted position, in accordance with an illustrativeembodiment of the present invention.

As noted above, the growing rod comprises a fixed rod 132, expansion rod120, and distraction unit housing 130. Each of these elements that formthe growing rod assembly 190 can be constructed from a biocompatibleplastic, metal, metal alloy, or a combination thereof. The biocompatiblemetals and metal alloys can be, for example, and without limitation,titanium, titanium alloy, stainless steel, cobalt chrome, or anycombination thereof. However, it will be clear to those skilled in theart, after reading this disclosure, how to make and use alternativeembodiments in which some of the elements of the growing rod assembly190 are made from a durable thermoplastic polymer, such as polyetherether ketone (PEEK).

In accordance with the illustrative embodiment, expansion rod 120 has aproximal portion that is slidably coupled to distraction unit housing130 and arranged with a drive gear mechanism, as further describedbelow. The extendible rod may be constructed to have a slightly smallerdiameter than that of the distraction unit housing 130 in order to allowthe extendible rod to telescopically slide in and out of the distractionunit housing 130. It will be clear to those skilled in the art, afterreading this disclosure, how to make and use alternative embodiments ofthe present invention in which the expansion rod 120, 122 can be adaptedto slide in and out of the distraction unit housing 130.

FIG. 3 depicts growing rod assembly 190 in a fully extendedconfiguration in accordance with an illustrative embodiment of thepresent invention. In this figure, expansion rod 120 has been fullyextended relative to distraction unit housing 130 in response to adoctor manually rotating a rotatable drive interface 140, 142 that isarranged on the outside of distraction unit housing 130. The doctor canalso fine-tune the length of growing rod assembly 190 by retractingexpansion rod 120 to the desired distraction length. The doctor canachieve this by manually rotating a rotatable drive interface 140, 142arranged on the outside of distraction unit housing 130 in the oppositedirection. The illustrative embodiment of expansion rod 120 is adaptedto allow for a minimum of three and a half years growth beforereplacement or removal is required. However, it will also be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments in which expansion rod 120 is adapted formore or less than three and a half years growth before replacement orremoval is required. These features of the present invention will bedescribed in more detail below, with respect to FIGS. 2 and 3 .

FIG. 4 is an enlarged top view of the growing rod assembly of FIG. 2 andFIG. 3 , in accordance with an illustrative embodiment of the presentinvention. Shown is the rotatable drive interface 140. This is arrangedon the outside of distraction unit housing 130 and is accessible to adoctor via a drive tool 150, which is an external driver. The rotatabledrive interface 140 is hexagon-shaped and is adapted to be received in acorrespondingly shaped recess of the external driver. The rotatabledrive interface 140 can be, for example, and without limitation anindustry standard 3.5 mm hex drive interface. Although the rotatabledrive interface 140 is depicted as hexagon-shaped, it will be clear tothose skilled in the art, after reading this disclosure, how to make anduse alternative embodiments of the present invention in which therotatable drive interface 140 can have any shape and size, so long as itcan be received by the recess of the external driver.

As briefly described above, rotatable drive interface 140 is adapted tobe accessed by an external driver from outside of distraction unithousing 130, 134. The rotatable drive interface is also adapted to bephysically coupled to and manually rotated by the external driver forextending and retracting the extendible rod relative to the distractionunit housing 130.

Detailed View of Growing Rod Assembly

Referring now to FIG. 5 is an exploded perspective view of the growingrod assembly 500 of FIGS. 2-4 , in accordance with an illustrativeembodiment of the present invention. The growing rod assembly 500provides a means for spinal lengthening for pediatric patients withearly-onset idiopathic & neuromuscular scoliosis. The growing rodassembly 500 provides precise distraction or contraction of the rod formultiple procedures over an extended period of years and providesgreater overall lengthening of the rod than other systems. The growingrod assembly 500 can accommodate increments and forces to match thegrowth pattern in scoliosis patients, as well as provide a means ofgrowth through either minimally invasive or external manipulation.

As used with growing rod assembly 500, the term “proximal” is defined asa direction toward the free end of the fixed rod 132, and the term“distal” is defined as a direction toward the free end of the expansionrod 120.

The growing rod assembly 500 includes a hollow housing 502 in the formof a hollow sleeve. An expansion tube 524 with internal threads 1022(See FIG. 10 ) is mounted in the hollow housing 502 and extends thelength thereof. In an embodiment, the threaded expansion tube 524 isconstructed from a biocompatible titanium alloy.

A housing cap 530 is attached to and is part of hollow housing 502. Afixed rod 132 extends along a longitudinal axis X-X′ (further shown inFIGS. 10 and 11 ) proximally away from the hollow housing 502, such thatthe housing cap 530 is located between the hollow housing 502 and thefixed rod 132.

In an embodiment, the fixed rod 132 is constructed from a biocompatibletitanium alloy or any other suitable biocompatible material. The fixedrod 132 has a distal end 546 (e.g., a conical distal end 548) that isfixedly connected to the hollow housing 502, an elongate body 516 (e.g.,a long 4.75 mm diameter cylindrical body), and a proximal end 412 (e.g.,a rounded proximal tip 414). In an embodiment, the fixed rod 132 can belaser welded to the hollow housing 502 or maybe otherwise be suitablyconnected or attached. The body 516 locks into pedicle screw 102, 104,106, 108, which may be any standard or custom screw. For example, body516 may be combined with a pedicle screw 172, 174, 176, 178 that accepts4.75 mm diameter rods (see FIG. 1 ). The rounded proximal tip 414 allowsthe fixed rod 132 to tunnel through tissue when the fixed rod 132 isbeing passed through the patient during implantation.

Referring now to FIGS. 5-11 , a growing rod assembly 190 in accordancewith embodiments of the present disclosure and its implantation into aspinal assembly will now be discussed.

In some embodiments, the growing rod assembly 190 includes the hollowhousing 502 in the form of a hollow sleeve. An expansion tube 524 withinternal threads 1022 (See FIG. 10 ) is mounted within the hollowhousing 502 and extends the length thereof. In an embodiment, thethreaded expansion tube 524 is constructed from biocompatible polyetherether ketone (PEEK) to advantageously reduce metallic wear debrisresulting from metal on metal contact and improve the imaging capabilityof the growing rod assembly 190.

A housing cap 530 is attached to and is part of the hollow housing 502.The expansion rod 520 extends along a longitudinal axis X-X′ proximallyaway from the hollow housing 502, such that the housing cap 530 islocated between the hollow housing 502 and the fixed rod 132.

As shown in FIG. 5 , the housing 502 includes upper portion 560A andlower portion 560B these fit together with a bevel pinion gear 534 and alock gear 536, both of which are rotatably mounted between the upperportion 560A and lower portion 560B. In another embodiment, the housingis a single housing portion without an upper portion 560A and lowerportion 560B. In an embodiment, the hollow housing 502 and the housingcap 530 are both made of biocompatible titanium alloy that are laserwelded together to align and protect the internal components. It iscontemplated, however, that suitable materials and modes of connectionor attachment may be used. The upper portion 560A has a housing topthru-hole 570A formed therein to allow access to the drive feature ofthe bevel pinion gear 534. Likewise, the second portion 560B has ahousing bottom thru-hole 570B.

Referring to FIG. 10 , a keyed expansion shaft bushing 522 is located inthe hollow housing 502 at a distal end 552 of the hollow housing 502. Akeyway 528 (shown in FIG. 5 ), for example, in the form of a flatsurface, is formed through the length of the expansion shaft bushing522. In an embodiment, the expansion shaft bushing 522 can beconstructed from biocompatible PEEK or other suitable materials and alsofunctions to reduce friction and prevent wear between an expansion rod520 and the hollow housing 502.

The expansion rod 520 is extendible through and from the hollow housing502 along a longitudinal axis X-X′. A pointed distal end portion 422 ofthe expansion rod 520 is adapted to extend outwardly from the distal end552 of the hollow housing 502. As shown in FIG. 11 , the pointed distalend portion 422 shows the expansion shaft bushing 522 has a cylindricalcross-section diameter D1 of about 4.75 mm in order to accommodatecommercially available pedicle screws that accept 4.75 mm diameter rods.However, it is contemplated that the diameter of the pointed distal endportion 422 may be any suitable diameter to mate with a correspondingpedicle screw system. The distal end portion 422 is located outside thehollow housing 502 and has a pointed tip similar to the pointed tip 424shown in FIGS. 2 and 3 that allows the tip to tunnel through tissue whenthe expansion rod 520 is being passed through the patient duringimplantation.

The expansion rod 520 has a proximal end portion 1114 with threadsengaged with the internal threads 1022 of the expansion tube 524. Theproximal end portion 1114 of the expansion rod 120 has a thread diameterD2, which is larger than the opening in the expansion shaft bushing 522so that when the expansion rod 520 is fully extended, as shown in FIG.11 , the expansion shaft bushing 522 retains the proximal end portion1114 in the hollow housing 502.

A central body portion 1024 of expansion rod 520 extends between thedistal end portion 1014 and the proximal end portion 1114 of theexpansion rod 520. In a fully contracted position, as shown in FIG. 10 ,at least a portion of the central body portion 1024 extends distally outof the hollow housing 502. In some embodiments, the central body portion1024 may have a diameter larger D2 than the diameter D1 of the distalend portion 422. The larger diameter is configured to accommodate amating to the keyway 528, for example, in the form of a flat surface(see FIG. 5 ) that engages the keyway 928 in the expansion shaft bushing522 to prevent rotation of the expansion rod 520 as the expansion rod520 extends out of or contracts into the hollow housing 502. Therefore,as the internally threaded expansion tube 524 rotates, the threadedconnection between the internally threaded expansion tube 524 and thethreaded proximal end portion 1114 of the expansion rod 520 causes theexpansion rod 520 to translate longitudinally along the longitudinalaxis X-X′.

Referring to FIG. 10 , a driver assembly is disposed in the hollowhousing 502 and the housing cap 530 and is adapted to translate, orextend, the expansion rod 520 along the longitudinal axis X-X′ in adistal direction from the hollow housing 502.

Turning to FIGS. 6 and 7 , in an embodiment, the driver assemblycomprises a gear mechanism. Further, in an embodiment, the gearmechanism comprises a right-angle drive gear assembly. In an embodiment,the right-angle drive assembly comprises a bevel pinion gear 534, a lockgear 536, and a bevel gear 746 rotatable about the longitudinal axisX-X′. In some embodiments, the pinion gear assembly 144 is located inthe hollow housing 502 between the fixed rod 132 and the expansion rod120. Vertically, the pinion gear assembly 144 is between the bottom ofthe hollow housing 502 and the housing cap 530, such that the bevel gear746 and the expansion tube 524 turn when the pinion gear assembly 144 isrotated. The bevel gear 746 and expansion tube 524 turn together as thebevel gear 746 is press fit into the expansion tube 524 and pinned inplace. In some embodiments, the bevel gear 746 and the expansion tube524 may alternatively be formed as one piece. As shown in FIG. 10 , thegear assembly is located between the housing cap 530 and the hollowhousing 502 and the fixed rod 132. The pinion gear 534 and the lock gear536 are both disposed perpendicularly to the bevel gear 746.

The bevel pinion gear 534 and the lock gear 536 are mounted between thehousing cap 530 and the hollow housing 502 and supported by pinionbushing 532, and lock gear bushing 538 (shown in FIG. 5 ), such that thepinion bushing 532 is mounted adjacent to the bevel pinion gear 534 andthe lock gear bushing 538 is mounted adjacent to the lock gear 536. Inan embodiment, the pinion bushing 532, and lock gear bushing 538 areconstructed from biocompatible PEEK or other suitable material and areused to reduce friction and prevent wear and metal on metal debris whenrotating the pinion gear 534 and/or the lock gear 536. In an embodiment,the pinion gear 534 has a rotatable drive interface 140, such ashexalobular drive interface. It is contemplated that other suitabledrive interfaces and drivers may be selected. The pinion gear 534includes teeth 734 on its upper end configured to mesh with teeth on thebevel gear 746 and ratcheting teeth 758 on its lower end configured tomesh with corresponding ratcheting teeth 740 on an upper end of the lockgear 536, as depicted in FIGS. 5-10 .

In some embodiments, a wave spring 540 may be disposed between the lockgear bushing 538 and the hollow housing 502 to exert an upward force onthe lock gear 536. The wave spring 540 acts as a locking mechanism forthe gears and is configured to prevent undesired back drive when thegrowing rod assembly 190 is implanted inside the patient. The piniongear 534 and the lock gear 536 share the same axis Y-Y′. Although theaxial movement of the pinion gear 534 is prevented, axial movement ofthe lock gear 536 between a first position (shown in FIG. 7 ) and asecond position (shown in FIG. 8 ) along the axis Y-Y′ is allowed. Inthe first position (i.e., a neutral/locked state), the wave spring 540forces the lock gear 536 upward such that teeth 738 at the bottom of thelock gear 536 are forced into engagement with the teeth of the bevelgear 746 while simultaneously maintaining engagement of the ratchetingteeth 740 of the lock gear 536 with the ratcheting teeth 758 of thepinion gear 534.

As a result, rotation of the pinion gear 534 and the bevel gear 746 isprevented. To unlock the gear, a surgeon inserts a driver 150 into therotatable drive interface 140 and applies a light downward force, whichflattens the wave spring 540 moving the lock gear 536 downward. As aresult, the ratcheting teeth 740 of the lock gear 536 are pushed out ofengagement with the ratcheting teeth of the pinion gear 758. Thisdownward motion of the lock gear 536 also pushes the lock gear teeth 738out of engagement with the teeth of the bevel gear 746, thus allowingthe pinion gear 534 and bevel gear 746 to turn freely, as shown in FIG.8 . When the surgeon removes the drive tool 150, the wave spring 540pushes the lock gear 536 back up into engagement with the bevel gear746, thereby automatically locking the rotation of the gears. Theratcheting interface between the lock gear 536 and the pinion gear 534(i.e., the interface between the corresponding ratcheting teeth 740,758) allows the surgeon to expand the expansion rod 520 withoutrequiring a downward force. However, collapsing the expansion rod 520requires the disengagement of the corresponding ratcheting teeth 740,758 by pushing the lock gear 536 downward, as explained above.

In some embodiments, a thrust bearing/bevel gear bushing 764 is disposedbetween the bevel gear 746 and the expansion tube collar 762 formed at aproximal portion of the expansion tube 524. The thrust bearing/bevelgear bushing 764 may be keyed to mate with a corresponding keyed surface(not shown) inside the hollow housing 502 to prevent translation of theexpansion tube 524 within the hollow housing 502. In some embodiments,and as shown in FIGS. 5-11 , the thrust bearing/bevel gear bushing 764can be a two-piece ring constructed from a biocompatible titanium alloyor other suitable material. The thrust bearing/bevel gear bushing 764serves to align the bevel gear 746 with the bevel pinion gear 534,reduce friction, ensure that the drive output gear 746 is held in placewithin the hollow housing 502, and prevent wear between the bevel gear746 and the hollow housing 502.

The drive output gear 746 forms an end (i.e., is integral with) of theinternally threaded expansion tube 524. As a result, the expansion tube524 rotates with the drive output gear 746, thereby translating theexpansion rod 520 along the longitudinal axis X-X′ as the bevel gear 746rotates to extend or contract the expansion rod 520 from or into thehollow housing 502 such that the growing rod assembly 190 expands orcontracts in length, depending on the direction of rotation of the bevelpinion gear 534.

The bevel gear assembly allows a surgeon to turn the pinion gear 534,which causes the expansion rod 520 to extend distally from the hollowhousing 502. In an embodiment, the bevel pinion gear 534, and the driveoutput gear 746 are both made of biocompatible titanium alloy (e.g.,TAV), and are designed with a pitch angle such that the bevel piniongear 534 is able to drive the drive output gear 746.

In some embodiments, the bevel gear assembly provides a reduction ratioof 0.8:1 or more. In some embodiments, the bevel gear assembly providesa reduction ratio of 1:0.75 such that for every full revolution of thebevel pinion gear 534, the bevel gear 746 rotates 0.75 revolutions. Inan embodiment, the ratio of the pinion teeth to the bevel gear teeth is15:20. In an embodiment, the bevel pinion gear 534 is rotated about one(1) complete revolution to achieve between about 1 mm and 1.25 mm ofexpansion or contraction of the expansion rod 520 from the hollowhousing 502, with the amount of growth based upon a goal measure of 1.8cm to 2.4 cm per year. Advantageously, a surgeon can fine-tune theamount of expansion by either increasing or decreasing the number ofrotations. This allows the surgeon to expand the expansion rod 520against large forces caused by the deformity. If a surgeon feels toomuch distraction has been incorporated, the growing rod assembly 190 canbe reduced by simply reversing the direction the bevel pinion gear 534is turned.

Similar to the growing rod assembly 500 described above, in anembodiment, the growing rod assembly 190 is 600 mm long with theexpansion rod 520 in a fully retracted position and 660 mm long with theexpansion rod 520 in a fully extended position, allowing for up to 60 mmof growth of the patient.

FIG. 9 is a cross-sectional view of an implantable rod assemblyaccording to embodiments of the present disclosure. This cross-sectionis taken through the hollow housing 502 of the rod assembly, theexpansion shaft bushing 522, and the expansion rod 520. In someembodiments, the expansion shaft bushing 522 has a central opening 924having a dual-lobe shape which receives the two lobes 922 of theexpansion rod 520 to lock the expansion rod 520 rotationally but allowthe rod to slide axially. In some embodiments, an outer surface of theexpansion shaft bushing 522 may have two lobes 922 as shown, whichinterface with the hollow housing 502 to prevent rotation of theexpansion shaft bushing 522 relative to the hollow housing 502. In someembodiments, the expansion shaft bushing 522 may include an expansionbushing slot 926 configured to allow for expansion of the expansionshaft bushing 522 over an end of the expansion rod 520 and sliding ofthe expansion shaft bushing 522 into a grooved portion (not shown inFIG. 9 ) of the expansion rod 520 during assembly. A pointed tip (notshown in FIG. 9 ) of the expansion rod 520 forces the expansion shaftbushing 522 open without harming the expansion shaft bushing 522 duringassembly. In some embodiments, the expansion shaft bushing 522 mayinclude two pieces (i.e., halves) (not shown) that are placed onto theexpansion rod 520 such that two lobes 922 are formed between the twopieces.

Smart Growing Rod System

Several “smart” features can be incorporated into the device design anduse of the device. These “smart” features provide critical data to thepatient, as well as the surgeon, to aid in determining the ideal rodlengthening interval and ensuring over-lengthening does not occur. These“smart” features would provide data on the implant's effect on thepatient's anatomy. This feedback could help tailor the course oftreatment specific to each patient. This information could improve thesafety of this device and expedite treatment for device-tolerantpatients.

By incorporating a real-time torque measuring sensor into the implant'sdriver instrumentation, input torque could be monitored whilelengthening the implant. One example of an implant driver torque wrenchwith Bluetooth capabilities is shown in FIG. 12 . A digital display 1202provides a real-time torque reading which is also wirelessly transmittedvia Bluetooth or other wireless near field communication technology.Examples of torque wrenches with Bluetooth capabilities are Tohnichi,Model Number CEM100N3X15D-G-BTS, and PROTO® Smart Torque Wrench.

Referring to the input torque table shown in FIG. 13 , shown are aseries of example measurements over time. A predicted length ofexpansion rod can also be determined based on the number of input turnsfrom implant driver torque wrench with Bluetooth capabilities and theratio of drive gears in pinion gear assembly 144, 146 illustrated inFIG. 1 . With this data in FIG. 13 , surgeons can carefully tailor thelengthening procedure to each individual patient. Monitoring when inputtorque rises substantially or at an exponential rate during growing rodexpansion will help surgeons identify when expansion has matched and orexceeded the patient's spinal growth. This torque data will helpsurgeons ensure sufficient lengthening has occurred and that the implantexpanded safely throughout the translation. This input torque data issaved and analyzed for any and all patients in the future. Trends areidentified using this torque data and could be used to create moreeffective lengthening plans for patients in real-time with theacquisition of each lengthening procedure's new data. The torque datacould be evaluated after each planned lengthening to help determine theremaining expansion plan based on the patient's anatomical response tothe implant. With substantial torque data captured and analyzed,predictive lengthening plans are created and adjusted throughout thepatient's course of care. This may be shown on a graph to help thesurgeon understand the relationship of input torque data and effectivelengthening plans, as discussed further below.

Turning now to FIG. 14 , this is similar to FIG. 8 described above thatillustrates an enlarged side elevational view of the gear assembly ofthe growing rod assembly of FIG. 6 with the housing omitted in a lockedor engaged position. Shown here are three features. A firstpiezoelectric force sensor 1410 disposed between the drive output gear746 and the thrust bearing/bevel gear busing 764, as shown. The firstpiezoelectric force sensor 1410 measures compression on expansion rod120. The second piezoelectric force sensor 1420 disposed between theexpansion tube collar 762 and housing (not shown) measures tension onthe expansion rod 120. The third feature is an electrical interface 1430disposed near rotatable drive interface 140, enables the surgeon to readthe forces on the first piezoelectric force sensor 1410 and the secondpiezoelectric force sensor 1420.

A simple circuit illustrated in FIG. 15 is a charge amplifier circuit1500 that converts the charge output from the piezoelectric forcesensors 1410, 1420, to a voltage output. The mathematical formulateaches the relationship between the charge produced, the applied force,compliance, and the material constant appears below, which is availablefrom the manufacture of the piezoelectric material. The compliance ofthe material is the inverse of Young's modulus: q=a*F*Ks. In thediagram, q is the charge source in parallel with the sensor capacitanceC_(P); C_(C) is the cable capacitance which is also in parallel with thesensor parameters; C_(F) and R_(F) are the feedback capacitance andresistance, respectively. It is this resistance that causes chargeleakage. LF355 is a commercially available input operational amplifier.The transducer's electrode cables 1415 and 1425 must have properinsulation and be short in length. Altering the cable length afterinstallation changes the capacitance; therefore, cutting or addingcabling requires knowledge of how to compensate for the new capacitance.

Referring to the input and expansion rod torque table shown in FIG. 16 ,is similar to the table in FIG. 13 above. In this table, the forces onthe expansion rod are also recorded. By incorporating piezoelectricforce sensors 1410, 1420 on either side of the bevel gear bushing 764,the device provides in-vivo feedback on when lengthening is necessary.By incorporating these piezoelectric force sensors 1410, 1420, axialcompression and tension on the implant's expansion rod 120 is measured.If the expansion rod 120 is subject to abnormal tensile forces over aperiod of time, this force is identified by the piezoelectric forcesensors 1410, 1420, and this data could be recorded and reported to anexternal device through the electrical interface 143. This tensile forceon the expansion rod 120 indicates that the patient's spine 10 has begunto outgrow the expansion rod 120, and a lengthening procedure would beadvised. The lengthening procedure would alleviate this tensile load onthe expansion rod 120. Similarly, if compressive forces are identifiedby the piezoelectric force sensors 1410, 1420, this indicates that theexpansion rod 120 was either expanded to a sufficient height in whichthe device influences the patient's spinal growth. If this compressiveforce were too substantial, this indicates the patient's spine 10 isunder significant distraction from the growing rod system 100, andoverlengthening may have occurred.

With input torsional data and force sensor data both in compression andtension being captured, these smart features provide significantclinical information in improving the safety and effectiveness of thisgrowing rod system 100. As these smart growing rod systems are used morefrequently, larger sets of data are gathered.

FIG. 17 is an example graph showing the values in the table of FIG. 16 .With proper data analysis, the torsional, compressive, and tensile loadsexperienced in the first expansion procedure predicts the majority ofthe patient's ideal treatment plan.

By monitoring input torsion, expansion rod tension, and expansion rodcompression, surgeons could optimize patients' lengthening proceduresindividually while maximizing the safety and effectiveness of eachlengthening procedure without risking over-expansion. As this device ismechanically actuated through a small, minimally invasive procedure, theimportance of limiting the number of times expansion is needed during astandard course of treatment is critical to the adoption andeffectiveness of this device.

Autonomous Growing Rod System

In this embodiment, Smart Growing Rod System is described above withreference to FIGS. 12-17 is further customized with a motor-drivenimplant. FIG. 17 is an example graph showing the values in the table ofFIG. 16 , in accordance with an illustrative embodiment of the presentinvention. The X-axis of FIG. 17 , are time periods 0, 1, 2, 3, etc.,and Y-axis is force F and length as shown. A lengthening procedureoccurs between each time period, i.e., between 0 and 1, 1 and 2, etc. Asshown in FIG. 17 , as the input torque increases as the expansion rod120 is lengthened to catch up to the spine's growth. The predictedlength should increase substantially at first but only increase slightlyduring the later lengthening procedures, i.e., periods 5, 6, etc. Theexpansion rod 120 would be held under tension at the start of thelengthening procedure as the patient's spine is “pulling up” on theexpansion rod 120 from its restricted growth. As the expansion rod 120is lengthened, this tension is relieved until spine growth has beenmatched. At this point, any further expansion of the growing rod wouldapply increasing compression on the expansion rod 120 as the device isfighting the spine. The intersection of the tension and compressionlines would be (in theory) when the expansion rod 120 was lengthened tothe exact length the spine had grown since the last lengthening. To theright of the intersection of these lines (where compression ramps up)would be the surgeon trying to achieve further correction and additionallength beyond that of the patient's current anatomical “height.” This isalso why tension ramps throughout each expansion as it faces moreresistance from the anatomy as the expansion is performed.

Turning now to FIG. 18 , shown is an autonomous growing rod motor-drivenimplant 1800. The features include a fixed rod, like the fixed rod 132shown in FIG. 1 is mechanically coupled with a housing, like distractionunit housing 130. The expansion rod 120 is housed partially within thehousing. This expansion rod translates freely out of the housing,“growing” the implant.

Several components of the autonomous growing rod motor-driven implant1800 may be placed within the housing (not shown). These componentsinclude a battery 1822, a circuit board 1820, a DC motor 1840, such as ahigh-torque DC motor with torsional sensors 1832, a thrust bearing/bevelgear bushing 764 piezoelectric force sensors 1410, 1420, the expansiontube 524, the expansion rod 520, and the keyed expansion shaft bushing522.

The circuit board 1820 will be comprised of the battery 1814, voltagecontrol circuit 1828, memory/storage device 1830, any circuitry such asa processor and memory needed for force/torsional sensor interpretation,such as that shown in FIG. 15 above, accelerometer 1826, and beBluetooth transceiver 1824. The battery 1814 of this autonomous growingrod motor-driven implant 1800 may be designed to provide power to theautonomous growing rod motor-driven implant 1800 for the duration ofimplantation. The battery 1814 may also be designed to be rechargedperiodically using a subdermal wireless charging pad. The patient couldposition a wireless charging pad under their spine 10 during rest orsleep, and the battery 1814 could be wirelessly charged through the softtissues of the posterior torso.

As shown in FIG. 18 , the circuit board 1820 controls the DC motor 1840while interpreting the force sensor data and monitoring the torqueapplied by the DC motor 1840. The accelerometer 1826, which is built-in,allows the autonomous growing rod to sense when normal locomotion isoccurring and when force sensor data should be ignored. When longperiods of no motion are sensed, like, during patient sleep, theautonomous growing rod motor-driven implant 1800 records the forcesensor data from piezoelectric force sensors 1410, 1420. By recordingdata throughout several hours of sleep on a regular basis, theautonomous growing rod motor-driven implant 1800 accurately determineswhether the patient's spine 10 has outgrown the length of the expansionrod or if the growing rod is putting too much axial tension on the spine10 and has been over-expanded. During rest, a compressive load on thepiezoelectric force sensor 1410 between the expansion tube 524 and thebevel gear bushing 760 indicates the expansion rod 520 is over-expandedand “pushing” the spine 10 upwards and fighting the distraction.Similarly, compressive forces sensed on first piezoelectric force sensor1420 between the expansion tube 524, and the housing indicates theexpansion rod 520 is under-expanded and the spine 10 is “pulling” theexpansion rod 520 upwards as the spine 10 continues to grow.

When the force sensor data suggests an expansion rod adjustment isneeded, the circuit board's voltage control circuit will supply thenecessary power to the DC motor using Pulse Width Modulation. Thiscircuit will control the speed and direction in which the DC motor willturn the expansion tube. While the DC motor operates, a feedback loop oftorsional data is monitored. This torsional data, as well as the forcesensor data, is monitored in real-time to safely and accurately expandor contract the autonomous growing rod motor-driven implant 1800 asneeded.

It is a known fact that the spine 10 slowly compresses over time eachday and slowly regains that lost height overnight. The Bluetoothtransceiver 1824 of this autonomous growing rod motor-driven implant1800 allows for recorded spinal growth and force sensor data to be sentout to a smart autonomous growing rod motor-driven implant 1800, throughnear field communications, such as Bluetooth, for further analysis. Asmore patients use this autonomous growing rod motor-driven implant 1800,more data could be captured and used to better predict and determine theideal expansion plan for each patient's individual anatomical responseto the autonomous growing rod motor-driven implant 1800. Each autonomousgrowing rod motor-driven implant 1800 would gain insight and become“smarter” as more data is collected and as the patient progressesthrough their course of treatment. Micro-adjustments to the growingrod's length on a regular basis could allow for the autonomous growingrod to account for the natural daily contraction and expansion of thespine 10 and optimize the overall spinal growth achieved from using thisautonomous growing rod motor-driven implant 1800.

The autonomous growing rod motor-driven implant 1800 is capable ofexpanding and contracting under substantial loads. These loads arelessened if expansion and contraction adjustments occurred only whilethe patient was stationary and horizontal. Auto-adjustments areprioritized during times of lower implant loading for adjusting thelength of the expansion rod 120. In order to achieve the translatingmotion of the expansion rod 120, the high-torque, low RPM DC motor candirectly drive an expansion tube. The interface between the DC motordrive shaft and the expansion tube 524 would house the torsional sensors1842 needed for torsional data capture. An expansion tube collar 762 andthrust bearing/bevel gear bushing 764 are placed between the DC motorand the expansion tube 524. Piezoelectric force sensors 1410, 1420 oneither side of the expansion tube collar 762 and thrust bearing/bevelgear bushing 764, this allows for compressive and tensile load datacapture.

The expansion tube 524 can be made of PEEK and be threaded on theinside. These expansion tube threads interact with a titanium expansionrod that is threaded into the expansion tube and keyed, similar to thekeyway 528. The end of the housing holds a PEEK bushing similar to 762with a similar keyed feature. Since the expansion rod 520 is heldrotationally by the keyed shape of the rod and the PEEK bushing, as theexpansion tube is rotated about the expansion rod, the threads translatethe expansion rod into or out of the expansion tube and housing based onthe direction of rotation. The expansion tube rotation, driven by the DCmotor 1840, translates the expansion rod 520 and uses the real-timeforce sensor and torsional data to accurately and safely expand orcontract the growing rod as needed to accommodate patients' anatomicalneeds. Since expansion rod translation is driven by expansion tuberotation, the unintended motion of the expansion rod is near impossible.High-torque, low RPM DC motors require considerable force to rotatefreely without electrical current being supplied to them. This beingsaid, safety locking features may be integrated into the autonomousgrowing rod motor-driven implant 1800 to further prevent unintendedexpansion or contraction of the growing rod.

Other embodiments of this autonomous growing rod motor-driven implant1800 could utilize alternative methods for expansion rod translation. Apneumatic cylinder paired with a micro-compressor could provide thedriving force needed to precisely expand and contract the autonomousgrowing rod motor-driven implant 1800. A hydraulic piston/cylindermechanism could also be used to drive this expansion and contraction.Finally, a shape memory alloy actuator with a locking clutch could alsobe utilized to expand and contract the autonomous growing rodmotor-driven implant 1800. Using focused radio frequency, the alloycould be externally heated, causing the alloy and, therefore, theautonomous growing rod motor-driven implant 1800 to expand. All of thesemethods of expansion/contraction could be monitored in real-time forprecise lengthening and to ensure the safe operation of the autonomousgrowing rod motor-driven implant 1800.

By monitoring and interpreting input torsion, expansion rod tension, andexpansion rod compression, the autonomous growing rod system couldtailor each adjustment to each patients' anatomical needs. Using datacapture, machine learning, and evaluating patient outcomes, theseautonomous growing rod motor-driven implant 1800 could improve on theircustomization of treatment to achieve better outcomes. The autonomy ofthe autonomous growing rod motor-driven implant 1800 limits the need foranesthesia and invasive procedures. The autonomous growing rodmotor-driven implant 1800's built-in Bluetooth capabilities allow forsmart autonomous growing rod motor-driven implant 1800 integration andapp-based tracking. This would allow surgeons to monitor patientprogress and allow for intervention and “manual” adjustment at any time.

FIG. 19 is a flow chart for managing an implant growing rod assembly ofFIG. 18 . The flow starts in step 1902 and immediately proceeds to step1904. In step 1904, the system operates an implantable motor controlcircuit for a DC motor with a torsion sensor and a drive output adaptedto translate an expansion rod along a longitudinal axis away from thehousing. The expansion rod includes a first piezoelectric sensor formeasuring a tension force thereon and a second piezoelectric sensor formeasuring a compression force thereon. The implantable motor controlcircuit includes a monitoring circuit for monitoring readings from thetorsion sensor coupled with the DC motor and readings from the firstpiezoelectric sensor and the second piezoelectric sensor. The processcontinues to step 1906.

In step 1906, data of tension force measured by the first piezoelectricsensor and data of a compression force measured by the secondpiezoelectric sensor is accessed. The process continues to step 1908.

In step 1908, an adjustment to be made to the expansion rod along thelongitudinal axis is calculated. The process continues to step 1910,which is an optional step.

In step 1910, data of previous adjustments made is accessed. This dataand the current force measurements are used by a learning algorithm tocalculate an adjustment to be made to the expansion rod along thelongitudinal axis. In one example, the data of the tension forcemeasured by the first piezoelectric sensor and data of torsion by the DCmotor measured by the torsion sensor is displayed. Also, it displays acalculated best fit curve for an adjustment to be made to the expansionrod along the longitudinal axis.

The process continues to step 1912. Otherwise, if the system is inautonomous mode, the process continues to step 1916.

In step 1912, a test is made to determine if the management of theimplant growing rod assembly is in autonomous mode. If the system is notin autonomous mode, the process continues to step 1914. In step 1914,the system waits until user input is received. The user input mayinclude further modifications to the adjustment to be made. The processcontinues to step 1916.

In step 1916, the DC motor is controlled to implement the adjustmentthat has been calculated, and the process ends in step 1918. In oneexample, the DC motor to implement the adjustment that has beencalculated used data accessed from the torsion sensor to monitor torqueoutput from the DC motor.

NON-LIMITING EMBODIMENTS

It is to be understood that the disclosure describes a few embodimentsand that many variations of the invention can easily be devised by thoseskilled in the art. Although the invention has been described in exampleembodiments, those skilled in the art will appreciate that variousmodifications may be made without departing from the spirit and scope ofthe invention. It is therefore to be understood that the inventionsherein may be practiced other than as specifically described. Thus, thepresent embodiments should be considered in all respects as illustrativeand not restrictive. Accordingly, it is intended that such changes andmodifications fall within the scope of the present invention as definedby the claims appended hereto.

What is claimed is:
 1. An implantable growing rod assembly comprising: abevel gear assembly disposed in a housing and adapted to translate anexpansion rod along a longitudinal axis away from the housing, whereinthe bevel gear assembly comprises: a bevel pinion gear having a firstset of teeth at an upper end and a first set of ratcheting teeth at abottom end, a lock gear disposed below and coaxial to the bevel piniongear, wherein the lock gear includes a second set of teeth at a bottomend and a second set of ratcheting teeth at an upper end, the second setof ratcheting teeth configured to mesh with the first set of ratchetingteeth; and a bevel gear perpendicular to the bevel pinion gear and thelock gear, wherein the bevel gear includes a third set of teeth thatmesh with the first set of teeth of the bevel pinion gear such thatrotation of the bevel pinion gear causes translation of the expansionrod along the longitudinal axis, wherein the lock gear is moveablebetween a first position, in which the first and second sets ofratcheting teeth are in engagement and the second and third sets ofteeth are in engagement, and a second position, in which the first andsecond sets of ratcheting teeth are not in engagement and the second andthird sets of teeth are not in engagement, a first piezoelectric sensordisposed between the bevel gear and the expansion rod, and behind thethird set of teeth for measuring a tension force on the expansion rod.2. The implantable growing rod assembly according to claim 1, whereinthe expansion rod comprises a distal end adapted to extend outwardlyfrom the housing.
 3. The implantable growing rod assembly according toclaim 1, wherein the bevel gear assembly is located in a housing capbetween the housing and a fixed rod.
 4. The implantable growing rodassembly of claim 1, further comprising: a wave spring disposed betweenthe housing and the lock gear and configured to exert an upward force onthe lock gear to bias the lock gear towards the first position.
 5. Theimplantable growing rod assembly according to claim 1, furthercomprising: a keyed bushing disposed in the housing and wherein theexpansion rod comprises a mating key located in the keyed bushing suchthat, as the expansion rod extends from the housing, the keyed bushingprevents the expansion rod from rotating.
 6. The implantable growing rodassembly according to claim 1, further comprising: a bevel gear bushingwith a first side and a second side disposed in the housing for guidingthe expansion rod along the longitudinal axis; and the firstpiezoelectric sensor disposed on the first side for measuring a tensionforce between the bevel gear bushing and the expansion rod.
 7. Theimplantable growing rod assembly according to claim 6, furthercomprising: a second piezoelectric sensor disposed on the second sidefor measuring a compression force between the bevel gear bushing and theexpansion rod.
 8. The implantable growing rod assembly according toclaim 7, further comprising: an implantable motor control circuit with aDC motor with drive output and a torsion sensor coupled therewith, thedrive output rotatably coupled to the bevel gear; and a monitoringcircuit for monitoring readings from the torsion sensor coupled with theDC motor and readings from the first piezoelectric sensor and the secondpiezoelectric sensor.
 9. An implantable growing rod assembly comprising:a bevel gear assembly disposed in a housing and adapted to translate anexpansion rod along a longitudinal axis away from the housing, whereinthe bevel gear assembly comprises: a bevel pinion gear having a firstset of teeth at an upper end and a first set of ratcheting teeth at abottom end, a bevel gear perpendicular to the bevel pinion gear, whereinthe bevel gear includes a second set of teeth that mesh with the firstset of teeth of the bevel pinion gear such that rotation of the bevelpinion gear causes translation of the expansion rod along thelongitudinal axis, a bevel gear bushing with a first side and a secondside disposed in the housing for guiding the expansion rod along thelongitudinal axis, and a first piezoelectric sensor disposed on thefirst side between the bevel gear and the expansion rod, and behind thesecond set of teeth for measuring a tension force between the bevel gearbushing and the expansion rod.
 10. The implantable growing rod assemblyaccording to claim 9, further comprising: a second piezoelectric sensordisposed on the second side for measuring a compression force betweenthe bevel gear bushing and the expansion rod.
 11. The implantablegrowing rod assembly according to claim 10, further comprising: animplantable motor control circuit with a DC motor with drive output anda torsion sensor coupled therewith, the drive output rotatably coupledto the bevel gear; and monitoring circuit for monitoring readings fromthe torsion sensor coupled with the DC motor and readings from the firstpiezoelectric sensor and the second piezoelectric sensor.
 12. Animplantable growing rod assembly comprising: a bevel gear assemblydisposed in a housing and adapted to translate an expansion rod along alongitudinal axis away from the housing, wherein the bevel gear assemblycomprises: a bevel pinion gear having a first set of teeth at an upperend and a first set of ratcheting teeth at a bottom end, a bevel gearperpendicular to the bevel pinion gear, wherein the bevel gear includesa second set of teeth that mesh with the first set of teeth of the bevelpinion gear such that rotation of the bevel pinion gear causestranslation of the expansion rod along the longitudinal axis, a bevelgear bushing with a first side and a second side disposed in the housingfor guiding the expansion rod along the longitudinal axis, a firstpiezoelectric sensor disposed on the first side for measuring a tensionforce between the bevel gear bushing and the expansion rod, a secondpiezoelectric sensor disposed on the second side for measuring acompression force between the bevel gear bushing and the expansion rod,and an implantable motor control circuit with a DC motor with driveoutput and a torsion sensor coupled therewith, the drive outputrotatably coupled to the bevel gear and a monitoring circuit formonitoring readings from the torsion sensor coupled with the DC motorand readings from the first piezoelectric sensor and the secondpiezoelectric sensor.
 13. The implantable growing rod assembly accordingto claim 12, wherein the implantable motor control circuit furtherincludes a processor coupled to memory, the processor executing programinstructions to access data of a tension force measured by the firstpiezoelectric sensor and data of a compression force measured by thesecond piezoelectric sensor; calculate an adjustment to be made to theexpansion rod along the longitudinal axis; and control the DC motor toimplement the adjustment that has been calculated.
 14. The implantablegrowing rod assembly according to claim 12, wherein the control the DCmotor to implement the adjustment that has been calculated includesaccessing data from torsion sensor to monitor torque output from the DCmotor.
 15. The implantable growing rod assembly according to claim 14,wherein the control the DC motor to implement the adjustment that hasbeen calculated is done autonomously without further intervention. 16.The implantable growing rod assembly according to claim 14, wherein thecontrol the DC motor to implement the adjustment that has beencalculated is done after receiving further manual input from an externalsource.
 17. The implantable growing rod assembly according to claim 14,wherein the processor executing program instructions further comprises:access data of previous adjustments made; and use a learning algorithmto calculate an adjustment to be made to the expansion rod along thelongitudinal axis.
 18. The implantable growing rod assembly according toclaim 14, wherein the processor executing program instructions furthercomprises: display each of the data of the tension force measured by thefirst piezoelectric sensor and data of torsion by the DC motor measuredby the torsion sensor; and display a calculated best fit curve for anadjustment to be made to the expansion rod along the longitudinal axis.